1. Field of the Invention
This invention relates to memory alloys and more particularly to memory alloys based on copper and nickel alloys having oxide inclusions.
2. Description of the Prior Art
Memory alloys based on copper and nickel are known and have been described in various publications (e.g. U.S. Pat. No. 3,783,037 and U.S. Pat. No. 4,019,925). Such memory alloys, which belong generally to the type having a .beta.-high temperature phase, are usually produced by fusion techniques.
When these alloys are cast they usually exhibit a coarse texture which becomes still coarser because of grain growth during subsequent annealing in the temperature range of the .beta.-phase solid solution and which cannot be reversed by hot working. As a result the mechanical characteristics, particularly elongation and notch ductility, of memory alloys produced in this manner are relatively poor and their field of application is limited.
It has already been proposed to produce memory alloys of the Cu/Zn/Al type by powder metallurgy, starting with previously prepared alloys corresponding to the final composition (e.g. M. Follon, E. Aernoudt, Powder-metallurgically processed shape-memory alloys, 5th European Symposium on Powder Metallurgy, Stockholm 1978, pp. 275-281). The prepared powder is encapsulated, cold compacted, hot compacted and extruded. However, this method is not suited for the production of compact and dense articles of Cu/Al/Ni and Ni/Al, because the powder does not cohere and the compacts disintegrate.
Therefore a need has continued to exist for improved memory alloys suitable for preparation by powder metallurgy.